Various laser procedures or operations require that the laser beam be properly focused to a specific focal point. For example, in ophthalmic laser surgery wherein eye tissue is to be photodisrupted or ablated in or on the tissue that is to be affected, the correct positioning of a focusing assembly used to focus a laser beam is very critical. Such ophthalmic surgical procedures include those in cornea, sclera, iris, the crystalline lens and related structures, vitreous, and retina, and for treatment of glaucoma. Focal depth precision is also required in many non-ophthalmic laser surgical procedures, such as applications in dermatology and even “surgery” in DNA to excise portions of chromosomes. Also, non-biologic applications, such as photolithography and micromachining require focal depth precision.
Even with calibration of a focusing element for a laser, which is made to vary according to the requirement of the surgical treatment pattern, the actual focal depth of the laser beam may differ from the desired focal depth for the treatment. Hence, there is a need for a closed-loop system that controls movement of a focusing assembly to a desired position and feedback validation that the desired movement of the focusing assembly has been achieved. In this manner, the depth position of a focal point may be precisely controlled.